The present invention relates to a linear motor.
As an example of a linear motor in which a movable element reciprocates linearly relative to a stator, the linear motor has an armature and at least one row of magnetic poles formed by juxtaposedly arranging a plurality of permanent magnets. The armature has a core which is constituted by laminating a plurality of electromagnetic steel plates and exciting windings. The core has a yoke that extends linearly in a direction orthogonal to the direction in which the electromagnetic steel plates are laminated, and a plurality of pole teeth that protrude from the yoke toward the magnetic pole row side and have magnetic pole surfaces opposed to the row of magnetic poles or magnetic pole row at their ends. A plurality of the exciting windings excite the pole teeth. In the linear motor of this type, however, large cogging force is generated. Thus, in order to solve this problem, there has been proposed a linear motor in which a processed metal plate was mounted so as to cover the core, as shown in FIG. 7 of U.S. Pat. No. 4,638,192. This processed metal plate has portions that protrude from both ends of the core in the reciprocating direction of the movable element. Each of these protruding portions has an arc-like curved surface so that a gap between the row of magnetic poles or magnetic pole row increases with increasing distance from the respective adjacent pole tooth.
However, in this linear motor, the metal plate is processed to form the arc-like curved surfaces. Thus, it was difficult to form the optimum arc shape for reducing the cogging force. Further, since the processed metal plate is employed, eddy current loss increases. Still further, the curved surfaces tend to deform due to an external force. For these reasons, variations in the quality of the linear motor were apt to occur.